J4mc [Now with invitations]
by cddgnoy
With J4mc, a player who opens a singleplayer world can let friends join through a public address, with no port forwarding.
What it does
J4mc connects a singleplayer world to a relay backend on the j4m.uk domain. Once a singleplayer world is opened to LAN, the relay hands it a public .j4m.uk hostname and passes Minecraft TCP packets between that world and anyone connecting via the hostname. The hostname and port are requested by the client and tied to the Minecraft account name.
The mod also adds invitations: a host can invite a friend who has the mod installed to join the world with a single click, without copying an address. The connection address has a clickable copy button, the interface is localized in English and Russian, and the player list can show ping. The host receives a notification when someone joins through j4mc. Third-party servers are not needed, and the mod works with whitelisted servers as well as singleplayer worlds.
Installing J4mc requires Fabric API. The mod is published for Fabric and Forge across 31 release versions, 1.16.2 – 26.3, and it runs on the client only, so servers need nothing from it.
Key features
Public LAN address
An opened singleplayer world receives a public .j4m.uk address that friends can use to connect.
One-click invitations
A host can invite a player who has the mod to join the world with one click from the game.
Relay tunnel
Traffic travels through the relay, which is only kept open while the world is open to LAN.
Connection address copy
A clickable button copies the connection address to the clipboard.
Join notifications and ping
The host is told when a player joins, and the player list shows each player's ping.
Gallery
Compatibility
Latest build for each game version and loader.
26.x5 of 5 versions with builds
1.21.x11 of 11 versions with builds
1.20.x5 of 5 versions with builds
1.19.x3 of 3 versions with builds
1.18.x1 of 1 version with builds
1.17.x2 of 2 versions with builds
1.16.x4 of 4 versions with builds
Only full game releases are shown. This mod publishes no snapshot builds.
Requirements
Dependencies declared by the latest file for each loader.
Required 1
Use cases
Who it’s for: Players who want to host a singleplayer world for friends without opening ports, and players who prefer sending invitations in the game over sharing addresses by hand.
How it compares
World Host is open source under the MIT License and runs on the client only, with files for Fabric, Forge, NeoForge and Quilt across 1.16.1 – 1.21.5. e4mc is open source under the MIT License and runs on client and server, with files for 1.17 – 26.3. Ngrok LAN is open source under the MIT License, client-side only and limited to Fabric for 1.18.2 – 1.20.2.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| J4mc [Now with invitations] | Fabric and Forge | 1.16.2 – 26.3 | Client-side only | 2026-10-11 |
| World Host | Fabric, Forge, NeoForge and Quilt | 1.16.1 – 1.21.5 | Client-side only | 2025-04-05 |
| e4mc | Fabric, Forge, NeoForge and Quilt | 1.17 – 26.3 | Client and server | 2026-10-01 |
| Ngrok LAN | Fabric | 1.18.2 – 1.20.2 | Client-side only | 2023-09-26 |
Questions
Does J4mc need Fabric API?
Do servers need to install J4mc?
Which loader and version should players use?
In the catalog
J4mc [Now with invitations] is one of 5,392 Social mods on ModsFinder, and one of 4,084 Social mods for Fabric. 8,071 mods support Minecraft 26.3.
Similar mods
What the author says
j4mc lets you open your singleplayer world to friends without port forwarding. Open your world to LAN, wait a moment, and j4mc gives you a public *.j4m.uk address that your friends can join through.
Official listing
- Modrinth page
- modrinth.com/mod/j4mc
- Owner
- cddgnoy
- Published
- 2026-08-13
- Updated on Modrinth
- 2026-10-11
- Facts verified
- 2026-10-15